题目:https://www.lydsy.com/JudgeOnline/problem.php?id=3631
树上差分;注意路径的结尾被多算了一次,最后要减去(不能提前减)。
代码如下:
#include<iostream> #include<cstdio> #include<cstring> using namespace std; int const maxn=300005; int n,a[maxn],head[maxn],ct,f[maxn],re[maxn],fa[maxn][22],bin[22],deep[maxn]; struct N{ int to,next; N(int t=0,int n=0):to(t),next(n) {} }edge[maxn<<1]; bool vis[maxn]; void dfs(int x) { for(int i=1;i<=18;i++) { if(deep[x]>=bin[i])fa[x][i]=fa[fa[x][i-1]][i-1]; else break; } for(int i=head[x],u;i;i=edge[i].next) { if(edge[i].to==fa[x][0])continue; deep[u=edge[i].to]=deep[x]+1; fa[u][0]=x; dfs(u); } } int lca(int x,int y) { if(deep[x]>deep[y])swap(x,y); int t=deep[y]-deep[x]; for(int i=0;i<=18;i++) if(t&bin[i])y=fa[y][i]; for(int i=18;i>=0;i--) if(fa[x][i]!=fa[y][i]) x=fa[x][i],y=fa[y][i]; if(x==y)return y; return fa[y][0]; } void dfs2(int x) { // cout<<x<<endl; if(vis[x])return; vis[x]=1; for(int i=head[x],u;i;i=edge[i].next) { u=edge[i].to; if(u==fa[x][0])continue; dfs2(u); f[x]+=f[u]; } } int main() { bin[0]=1; for(int i=1;i<20;i++)bin[i]=(bin[i-1]<<1); scanf("%d",&n); for(int i=1;i<=n;i++)scanf("%d",&a[i]); for(int i=1,x,y;i<n;i++) { scanf("%d%d",&x,&y); edge[++ct]=N(y,head[x]);head[x]=ct; edge[++ct]=N(x,head[y]);head[y]=ct; } dfs(1); for(int i=2;i<=n;i++) { f[a[i-1]]++;f[a[i]]++;re[a[i]]++; int l=lca(a[i-1],a[i]); f[l]--;f[fa[l][0]]--; } dfs2(1); for(int i=1;i<=n;i++) printf("%d ",f[i]-re[i]); return 0; }